Chalcogenides of copper and/or silver have special utility for thermoelectric conversions of heat energy to electrical energy, partly because of the high temperatures to which they may be heated. But these high temperatures also make it difficult to form long-lasting, low-impedance electrical contacts to thermoelectric legs made from the chalcogenides. At the desired high temperature, common metal electrode materials tend to react or interact with the leg. For example, if copper, silver, and iron, which have been successfully used in other thermoelectric constructions, are used as hot-junction electrodes for P-type legs of the described class of compositions, they will migrate into and even through the leg to reduce thermoelectric conversion properties.
Another material previously used as an electrode material--platinum--reacts with copper to form a copper-platinum alloy dispersed as a second phase in the leg, thus removing copper from, and disturbing the carrier concentration of, the chalcogenide phase in which the thermoelectric voltage is generated. Several other materials, such as nickel, tantalum, and niobium, react with selenium at the desired high temperatures to also disturb the carrier concentration of the leg.
Carbon electrodes are chemically inert toward the described family of alloy compositions, and therefore can be useful with them under some conditions. But carbon does not have the desired mechanical strength and conductivity properties of a metal electrode, so that it also is not an adequate answer to the need for useful hot-junction electrode members for the described alloy composition.